Antenna devices disclosed in, for example, Patent Literature 1 and Patent Literature 2 are antenna devices for an FM band and for an AM band mountable on a vehicle body. In the antenna device disclosed in Patent Literature 1, an antenna base and an antenna element including two kinds of helical antenna portions are arranged in a shark fin antenna case. The antenna element includes a first helical portion closer to the antenna base and a second helical portion farther from the antenna base. The first helical portion is formed of a rail-like pattern or a plate-like conductive member. Meanwhile, the second helical portion has a surface area per unit length that is larger than that of the first helical portion, and is formed of a linear pattern, a solid pattern, a solid pattern and wire, or a plate-like conductive member bent so as to be substantially U-shaped (oblong helical element).
Further, in the antenna device disclosed in Patent Literature 2, the antenna element includes a helical antenna element and a plate-like element. The antenna element is wound about a virtual axis extending from an antenna base toward a top portion of an antenna device for a vehicle. The plate-like element is a conductive plate, and is arranged on an open end side of the helical antenna element so as to cover the top portion while being electrically connected to the open end side of the helical antenna element and so as to have, with the virtual axis, a positional relationship of intersecting each other perpendicularly or obliquely.